1. Field of the Invention
The present invention relates to an ink jet ink reservoir used in an ink jet recording apparatus.
2. Description of the Related Art
Conventionally, an ink jet recording apparatus has an ink jet head cartridge having a general construction wherein an ink reservoir (sometimes referred to as “ink tank”) for storing an ink and an ink jet recording head portion for ejecting the ink to conduct printing are connected to each other directly or via an ink-feeding member such as a tube. In such an ink jet recording apparatus, resin materials, metallic materials, rubber materials and the like have heretofore been used for members always contacting with an ink. Of these materials, the resin materials have preferably been used from the viewpoints of cost and processability.
Examples of the resin materials include polyolefins, ABS (acrylonitrile butadiene styrene), PS (polystyrene), PET (polyethylene terephthalate) and PVC (polyvinyl chloride). Of these resin materials, polyolefin resins are particularly preferably utilized from the viewpoints of chemical resistance, recyclability, transparency, easiness of molding and cost. Examples of the polyolefin resins include polyethylene, polypropylene and ethylene-propylene copolymers.
In the case of polyolefin resins, a chloride compound derived from a chlorine-based Ziegler-Natta catalyst used at the time of resin synthesis remains in the polymer and is corroded and yellowed. Therefore, it is known that fatty acid salts or hydrotalcites may be added as a neutralizer. Further, to enhance transparency, it is general to add a nucleating agent that facilitates the production of resin crystal cores and grows fine crystals. A lubricant such as wax may be added to improve mold release properties after molding.
Further, it is generally known that various antioxidants are added to a polyolefin resin for the purpose of stabilizing the quality. Particularly, in a process for melting and drawing a resin into a fiber form as well as in a process of the hot melt molding, autoxidation of the resin (resin deterioration) is likely to occur due to heat-induced oxygen radical, since the resin has a larger surface area. Therefore, it is known to use a phenolic antioxidant or a combination of a phenolic antioxidant and a phosphorus antioxidant. A phenolic antioxidant with a hindered phenol skeleton instantly captures oxygen radical generated by heat to be a peroxide. The generated peroxide becomes a quinone, which yellows a resin, causing difficulties in reproducing and recycling the resin. However, if a phosphorus antioxidant is used in combination therewith, the phosphorus antioxidant reduces the peroxide thereby to reproduce the original phenolic antioxidant, thus facilitating resin recycling.
It is known that a sulfur antioxidant is used additionally after molding to prevent the deterioration by oxygen radical generated by light, heat, ozone, etc. (for example, “Kobunshi tenkazai no shin-tenkai (New development of Polymeric Additives” edited by Chemical Society of Japan, Society of Polymer Science, Japan, published by Nikkan Kogyo Shimbun, Ltd., Sep. 30, 1998).
However, the above conventional technologies have the following problems. A phosphorus antioxidant functions as a reducing agent under a heated environment mainly at the time of molding, and a phosphorus atom is changed from trivalent to pentavalent to capture oxygen. The generated pentavalent phosphorus compound has a higher polarity than the trivalent one, and is easily dissolved in an aqueous ink jet ink (hereafter referred to simply as “ink”). The generated pentavalent phosphorus compound is in contact with an ink for a long period of time or may be dissolved in the ink even for a short period if placed at a high temperature. The solubility of a pentavalent phosphorus compound in an ink is dependent on the kind of color material and solvent composition in the ink, or pH though the reason for that is yet unknown. Further, the phosphorus compound is precipitated on stainless filter provided at several locations of an ink flow path of an ink jet printer for filtrating dust thereby to prevent the flow of ink, finally leading to a problem of printing defects caused by insufficient ink supply.
Japanese Patent No. 3575034 discloses that use of a phenolic antioxidant with an isocyanurate skeleton enhances wettability of an ink reservoir or ink-contacting member, thus improving ink tracking property. Further, the Patent discloses that a phosphinopropionate compound is effective as an antioxidant. Japanese Patent No. 3308113 discloses that an acidic phosphonic acid derivative, which is the hydrolysate of an oxide as a phosphorus antioxidant, has a mold release effect as an internal lubricant. However, both patents do not refer to the solubility of a phosphorus antioxidant in an ink jet ink.
Japanese Patent Application Laid-Open No. H11-240182 discloses in its Examples that an absorber composed of a polypropylene core material and a polyethylene sheath material is mounted on an ink tank prepared from NORIL (modified polyphenylene oxide) manufactured by GE plastics. Sulfur, phenolic and phosphorus antioxidants are added to each of the polypropylene core material and polyethylene sheath material. To the core and sheath materials, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite and tris(2,4-di-t-butylphenyl)phosphite are added, respectively, as phosphorus antioxidant.
The above ink tank was filled with an ink and allowed to stand at room temperature for several months. Thereafter, the printing was performed. The discharge of the ink was gradually reduced and finally stopped completely. This took place because of clogging of oxides of bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite used in the core material at a stainless filter located at a connection part between the ink tank and a tip tank (a structure carrying an ink jet head).